http://en.wikipedia.org/wiki/Balfour_Declaration_of_1917#Military_and_political_context
The war, in a grisly virtual stalemate at this point in time, found both Germany and Britain actively making overtures to the Zionist Movement in order to enlist the resources of this group in assisting their cause. Both sides were well aware of the significant Zionist influence within Bolshevik Russia, the United Kingdom, Germany and the United States. Further, Britain recognized that the natural sentiment of many European Jews was, in fact, with Germany and Austria-Hungary. Following the logic that “my enemy’s enemy is my friend” European Jews tended to view the Central Powers favorably given their role in defeating the overtly anti-Semitic Tsarist government in Russia. Well aware of this sentiment, Imperial Germany during this same period was actively courting the Zionist movement, both domestically and internationally, but was circumscribed in this effort by the fact that Palestine was then a component of the Ottoman Empire – a key ally of Germany within the Central Powers.
By the Summer of 1917, the world had been at war for three years. All major belligerents were facing the common issues of unbelievable casualty levels, the deprivations of an increasingly effective blockade, dwindling financial resources and the unthinkable specter of actually losing the war. No tactic or strategy was beyond consideration if it offered a reasonable chance to gain advantage over the other side.
At the same time the Zionist movement was very active in all forms of negotiations to convince one or more of the major powers to support the goals of the Zionist movement - namely support for Jewish migration to Palestine. Active negotiations were going on in Constantinople, Berlin, Paris, London, New York and Washington. As events turned out, Zionist efforts first proved successful in London.